The present invention relates to pistons for internal combustion engines, particularly pistons made of light alloy, of the type including a cylindrical skirt the wall thickness of which, is of increased thickness at two diametrically opposite points to form the so-called "bosses" each of which has a hole extending radially with respect to the cylindrical piston skirt. The two holes are axially aligned with one another and are intended to receive and support the end of a gudgeon pin by means of which the piston is attached to one end, the so called little end, of a connecting rod, the other end, the so-called big end, of which is journalled on the crankshaft.
Pistons of the above described type are particularly susceptible to damage due to stresses to which they are subject because of the elevated temperatures which are attained within the cylinders when the engine is running. These stresses are due above all to the relatively large differences between the temperatures which are reached by the different parts of the piston wall when the engine is running. In particular the two above mentioned zones of thickened skirt wall (the so-called "bosses") reach mush higher temperatures than the adjacent parts of the skirt of the piston, due to the greater mass of these bosses.
Normally, in order to encourage the cooling of the interior cavity of the piston, defined by the piston skirt, and in particular to encourage the cooling of the bosses, the oil which serves for the lubrication of the engine is used as a coolant; this is achieved by allowing a part of the lubrication oil to escape from the associated crank of the crankshaft of the engine, this oil being thrown by centrifugal force against the inside wall of the piston skirt.
This cooling system, however, does not give satisfactory results from the point of view of the reduction of the sharp temperature differences which give rise to the above mentioned heat originated stresses.